Handbook Of Shaft Alignment Episode 1 Part 9 potx

FIGURE 5.46 Cleaning the pump feet using 180 grit emery cloth wrapped around a 1=8 in. thick steel bar and ‘‘sawing’’ back and forth to clean the underside of the machine foot and the base plate at the same time. FIGURE 5.47 The underside of this motor foot is ‘‘hollow.’’ Make sure for using the right size shims to get as much contact as possible here. Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C005 Final Proof page 210 26.9.2006 8:36pm 210 Shaft Alignment Handbook, Third Edition 6. Once all of the bolts have been loosened, review what you observed when each bolt was loosened. If more than 2–3 mils of movement occurred when just one of the bolts was loosened, then there is probably a soft foot condition at that foot only. Remove any soft foot shims under that foot and remeasure four points around that bolt-hole FIGURE 5.48 Soft foot correction shim stack. FIGURE 5.49 Soft foot correction shims for a motor. FIGURE 5.50 Soft foot correction shims stack. Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C005 Final Proof page 211 26.9.2006 8:36pm Preliminary Alignment Checks 211 with feeler gauges and install a flat shim or shim wedge to correct the observed condition. If more than 2–3 mils of movement were noticed when several of the bolts were loosened, then there is probably a soft foot condition at each one of those feet. Remove any soft foot shims under those feet and remeasure four points around those bolt-holes with feeler gauges and install flat shims or shim wedges to correct the observed condition. 7. Repeat the procedure if additional corrections are required. 5.6.3 SHAFT MOVEMENT METHOD (THIRD CHOICE) 1. Tighten all of the foot bolts holding the machine in place. 2. Attach a bracket to one shaft, place a dial indicator on the topside of the other shaft, and zero the indicator at mid-range. 3. Sequentially loosen one-foot bolt at a time observing for any movement at the indicator when each bolt is loosened. 4. If there were more than 2–3 mils of movement when only one of the bolts were loosened, then there is probably a soft foot condition at that foot only. Remove any soft foot shims under that foot and remeasure four points around that bolt-hole with feeler gauges and install a flat shim or shim wedge to correct the observed condition. If more than 2–3 mils of movement were noticed when several of the bolts were loosened, then there is probably a soft foot condition at each one of those feet. Remove any soft foot shims under those feet and remeasure four points around those bolt-holes with feeler gauges and install flat shims or shim wedges to correct the observed condition. 5. Repeat the procedure if additional corrections are required. 5.6.4 SINGLE BOLT–SINGLE INDICATOR METHOD (LAST CHOICE) 1. Tighten all of the foot bolts holding the machine in place. 2. Place a dial indicator at one of the feet on the machine case. Anchor the dial indicator to the frame or base and place the dial indicator stem as close as possible to the bolt-hole, insure that the stem is touching the top of the foot, and zero the indicator at mid-range. 3. Loosen the bolt where the indicator is located, watching the indicator at that foot for any movement. If more than 2–3 mils of movement are detected, there is probably some soft foot still remaining at that foot. Remove any soft foot shims under that foot and remeasure four points around that bolt-hole with feeler gauges and install a flat shim or shim wedge to correct the observed condition. Retighten the bolt. 4. Sequentially move the indicator to each one of the feet, loosening that bolt and watching the indicator for any movement. If more than 2–3 mils of movement are detected when each bolt was loosened, there is probably some soft foot still remaining at that foot. Remove any soft foot shims under that foot and remeasure four points around that bolt- hole with feeler gauges and install a flat shim or shim wedge to correct the observed condition. Retighten each bolt. 5. Repeat the procedure if additional corrections are required. Once the soft foot has been corrected, the shims will stay there for the rest of the alignment process. We may be adding more shims later on to change the height or ‘‘pitch’’ of the machine case but the shims used to correct the soft foot condition will remain in place. As illustrated in Figure 5.51 through Figure 5.53, a soft foot condition can occur on other machinery components besides the machine case itself, in this instance, it is a pillow block bearing and its mating pedestal. Figure 5.54 shows a turbine bearing with lateral support Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C005 Final Proof page 212 26.9.2006 8:36pm 212 Shaft Alignment Handbook, Third Edition FIGURE 5.51 Soft foot correction shims for a pillow block bearing on a fan. FIGURE 5.52 Checking for lift with a magnetic base and dial indicator on a machine foot. FIGURE 5.53 Checking for lift with a magnetic base and dial indicator on a fan frame. Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C005 Final Proof page 213 26.9.2006 8:36pm Preliminary Alignment Checks 213 plates that are bolted to the condenser shell. There was uneven contact between the lateral support plates and the condenser shell flange. Soft foot shims had to be installed here to provide sufficient contact to achieve the desired lateral stiffness. Figure 5.55 through Figure 5.58 show another pillow block bearing that was not making adequate contact. Figure 5.55 shows the underside of the lower pillow block casting. Notice that it too is ‘‘hollow.’’ To determine where the lower casting was not touching the pedestal, 5-mil thick shim strip were placed on the pedestal to elevate the lower casting a known distance. Plastigage was then placed at the areas of contact, the bearing set down and the bolts tightened slightly. After loosening the bolts and removing the lower pillow block casting, the amount of crush was measured using the guide on the Plastigage container sleeve as shown in Figure 5.57. Shims were then installed where the gap was observed to be over 5 mils. Figure 5.58 shows a lift check made on the pillow block to insure the lack of contact problem was corrected. 5.7 OTHER METHODS FOR CORRECTING SOFT FOOT PROBLEMS For many of the readers who are reading about this problem for the first time, there is a great tendency to disbelieve that this malady actually exists. Be forewarned, this is a time consum- ing, frustrating process that frequently can consume more time than actually aligning the rotating machinery itself. Despite the fact that two out of three pieces of rotating machinery have a soft foot problem, very few solutions have been forwarded on how to correct this problem easily. It does seem rather silly to cut U-shaped shims into strips, L-shapes, J-shapes, or shortened U-shapes to correct this problem but precut, U-shaped shims are commonly used in industry to adjust the position of rotating machinery in the process of aligning equipment. But it is not possible to correct a wedge-shaped gap condition with a flat piece of shim stock. Since many FIGURE 5.54 Soft foot shims installed on turbine bearing lateral support plates. Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C005 Final Proof page 214 26.9.2006 8:36pm 214 Shaft Alignment Handbook, Third Edition FIGURE 5.55 Underside of pillow block bearing lower casting. FIGURE 5.56 Installing shims and Plastigage for contact check. Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C005 Final Proof page 215 26.9.2006 8:36pm Preliminary Alignment Checks 215 people only have this precut shim stock available to them, then the only way to construct a wedge is to ‘‘stair-step’’ pieces of shims together to construct the wedge that is needed. For people who have a lot of time on their hands, they could actually machine a custom wedge shape shim after they ‘‘mapped’’ out the gaps at each foot. People have actually done this. There have been a few attempts to create a device that automatically corrects for a soft foot condition. Proprietary plastic shims were experimented within the 1990s but they did not seem to meet the requirements satisfactorily. They did provide some damping between the machine and the base plate however. Before that there were ‘‘peel away’’ shim blocks. Thin shim stock was made into a multi- layer sandwich, where several thin shims were bonded together with a thin adhesive layer. People would then peel away as many layers as they needed and could trim each layer to form a wedge if desired. Since nonhardening adhesive was used, applications on machinery that ran hot would begin to debond the layers. One always hoped the adhesive would not flow and squeeze out since it had a thickness to it also. FIGURE 5.57 Measuring the crushed Plastigage. FIGURE 5.58 Checking for lift after installing the noncontact (i.e., soft foot) correction shims. Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C005 Final Proof page 216 26.9.2006 8:36pm 216 Shaft Alignment Handbook, Third Edition One idea from a colleague suggested that you take two 10-mil thick shims, mix up some epoxy resin and hardener, spread the epoxy on one side of a shim, and then make a shim ‘‘sandwich,’’ install it under the foot, and then let it harden. In the event that too much epoxy was applied, the idea suggested that you can put the shim inside a plastic bag so the excess epoxy would flow into the bag and not adhere the machine to its base plate. Then, after the epoxy cured, it is essential to remove the bagged shim, trim away the squeezed out epoxy, remove the plastic bag, and reinstall the shim. I tried that one time and got yelled at for spending too much time ‘‘goofing around’’ and not getting the alignment job done. Another similar yet more elegant idea was developed by another colleague. These devices were dubbed ‘‘foot plane compensators’’ and are shown in Figure 5.59 and Figure 5.60. The underside of the foot plane compensator has channeling to allow epoxy to flow into the cavity. An O-ring seals the perimeter to prevent the epoxy from flowing out. A special bolt is used to attach the foot plane compensator to the underside of every foot on a machine and then the machine is set down onto its base plate. Tubing is then placed into one of the openings on the side of the foot plane compensator and epoxy is injected into the cavity. Once the epoxy sets and hardens the foot plane compensator to the base plate, the special FIGURE 5.59 Foot plane compensator. Underside view showing epoxy channels. (Courtesy of Max Roeder Consulting, Inc., Danville, IN.) FIGURE 5.60 Foot plane compensator. Injecting epoxy into the channels. (Courtesy of Max Roeder Consulting, Inc., Danville, IN.) Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C005 Final Proof page 217 26.9.2006 8:36pm Preliminary Alignment Checks 217 bolt is removed and the original foot bolts are then installed and the final alignment process then continues. However, there is one problem with all of the above ideas. As mentioned in Figure 5.40, after the soft foot has been corrected, you may very well install additional shims under the machinery feet to correct a misalignment condition. What if, later on during the final alignment process, you find out that you need to add 300 mils of shims under the outboard bolting plane of a machine and 5 mils of shims under the inboard bolting plane? If you raise one end of a machine significantly higher than the other end, will it introduce a soft foot problem. And if the angular pitch is severe enough, it is essential to correct the soft foot problem, just introduced into the machine–base plate interface. Whatever soft foot correction device or mechanism is invented to automatically correct this problem, there are eight issues (eventually ‘‘features’’ if successful) that need to be addressed by the brave inventor: 1. The vast majority of soft foot problems are nonparallel gap situations. 2. One or more than one machine foot may not be making contact whether parallel or nonparallel conditions exist between the machine and its point of contact on the base or frame. It must therefore be recognized that soft foot is not a surface area problem, but a volume problem. 3. It is possible that a soft foot condition could be introduced when adding more shims under one end of a machine case than the other end when attempting to correct a misalignment condition. Therefore the device has to change its shape to account for an intended angular pitch on the machine casing. 4. Thermal warpage of a machine base or frame can occur during operation that would alter the soft foot condition as observed during the off-line condition. 5. Be ‘‘thin’’ enough to fit under all of the currently installed rotating machinery without having to make major frame, machine case, or piping alterations. 6. Maintain its shape and volume for long periods of time under vibratory forces, extreme pressure from torqued foot bolts, and possibly high temperatures from the machine during operation. 7. Be relatively inexpensive. 8. Easy to install or remove and have little or no maintenance required. Perhaps someday the solution will come in a material that can alter its shape and volume when an electrical charge is applied to it. Or maybe people are looking at this in the wrong way. The above solutions are macroscopic in approach. Maybe a microscopic approach is needed. Perhaps thousands of tiny wedges or pistons or solenoids can arrange themselves in such a manner to solve the eight issues mentioned above. Nanotechnology may provide the answer. But before these pie-in-the-sky approaches are explored, the first thing is to educate the people designing, purchasing, installing, and aligning rotating machines that this issue exists. Disappointingly, not enough people are aware that they even have this problem. Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C005 Final Proof page 218 26.9.2006 8:36pm 218 Shaft Alignment Handbook, Third Edition 6 Shaft Alignment Measuring Tools An alignment ‘‘expert’’ is someone who is knowledgeable about the myriad of measuring tools available for shaft alignment and also knows how to perform all five of the shaft positional measurement methods and understands the limitations of them. There are advan- tages and disadvantages to each one of these methods as discussed in Chapter 10 through Chapter 15. There is no one method or measuring device that will solve every alignment problem that one can possibly encounter on all the various types of rotating machinery drive systems in existence. It is important to understand each one of these techniques so you can select the best measurement method for the alignment situation confronting you. In many cases, two (or more) different techniques could be used to make shaft centerline positional measurements on the same drive system. Every once in a while, people who capture a set of shaft alignment readings using one of these techniques or measurement tools will run across a situation where the measurements they have taken do not seem to make sense. Knowing how to perform shaft positional measurements, a different way can verify whether the data from the initial technique in doubt are valid. Since the machinery shafts can only be in one position at any point in time, the data from two or more measurement methods should indicate the same shaft positional information. For example, if you have captured a set of readings with a laser alignment system and you do not believe what the system is telling you then take a set of reverse indicator readings. If the two sets of readings agree, then the measurement data are probably correct. If they do not, then it would be wise to determine why there is a discrepancy between the two methods before you continue. If you do not investigate the cause, you may incorrectly position the machinery based on bad measurement data. Therefore, knowing all the methods offers you a choice of which one you would like to do and, if necessary, compare one method to another, or validate one against the other. Since shaft alignment is primarily concerned with the application of distance measurement, this chapter will begin by covering the wide variety of tools available to measure dimensions. Next, the five currently known shaft alignment measurement techniques commonly employed for rotating machinery shafts connected together with flexible couplings will be shown. Two other shaft alignment techniques used on rotating machinery shafts connected together with rigid couplings are explained. The illustrations for these techniques show utilizing mechanical dial indicators as the measurement device but any measurement device with an accuracy of 1 mil (or better) could be used. It is recommended that you understand each of these basic measurement methods shown in Chapter 10 through Chapter 14 since every alignment measurement system in existence utilizes one or more of these methods regardless of the measurement sensor used to capture the shaft position information. Keep in mind that this chapter covers one small but important facet of shaft alignment, measuring the relative positions of two rotating machinery shafts. In other words, these Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C006 Final Proof page 219 26.9.2006 8:51pm 219 [...]... the location of the instrument is stable and to allow some time Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C006 Final Proof page 230 230 26 .9. 2006 8:51pm Shaft Alignment Handbook, Third Edition FIGURE 6 .13 Scale targets mounted on an electric generator bearing Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C006 Final Proof page 2 31 26 .9. 2006 8:51pm Shaft Alignment Measuring... movement Figure 6 .10 and Figure 6 .11 show the FIGURE 6 .10 Optical tilting level and jig transit Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C006 Final Proof page 228 228 26 .9. 2006 8:51pm Shaft Alignment Handbook, Third Edition FIGURE 6 .11 Jig transit (Courtesy of Brunson Instrument Co., Kansas City, MO With permission.) two most widely used optical instruments for machinery alignment This... Interferometers Charge couple device (CCD) Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C006 Final Proof page 2 21 Shaft Alignment Measuring Tools 26 .9. 2006 8:51pm 2 21 FIGURE 6 .1 Standard linear rulers Many of these devices are currently used in alignment of rotating machinery Some could be used but are not currently offered with any available alignment measurement systems or tooling but are... length, thread angles, thread depth, Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C006 Final Proof page 224 224 26 .9. 2006 8:51pm Shaft Alignment Handbook, Third Edition Measure inside dimensions here Start here Notice that the “zero” mark is between 0.750 in and 0.775 in Thousandths scale 0 0 1 2 3 4 5 6 7 5 8 9 1 10 1 2 15 3 4 5 20 6 7 25 8 9 2 Ruler Measure outside dimensions here Then... screws to first adjust the circular level in one direction 30 10 5 40 0 5 10 50 60 And then these two screws for the other direction 10 5 5 0 10 40 30 60 50 FIGURE 6 . 19 How to level a tilting level or jig transit, part 1 through part 4 manufacturer of alignment measurement systems uses this type of transducer for shaft alignment purposes 6.2 .10 OPTICAL ENCODERS Optical encoders are essentially pulse counters... accuracy is equivalent to the level of correction capability (i.e., shim stock cannot be purchased in thickness less than 1 mil) Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C006 Final Proof page 226 226 26 .9. 2006 8:51pm Shaft Alignment Handbook, Third Edition FIGURE 6.7 Dial indicator 6.2.6 OPTICAL ALIGNMENT TOOLING Optical alignment tooling consists of devices that combine low-power... 8:51pm Shaft Alignment Measuring Tools 2 31 FIGURE 6 .14 Scale targets mounted on compressor casing near their centerline of rotation FIGURE 6 .15 An optical micrometer (Courtesy of Brunson Instrument Co., Kansas City, MO With permission.) Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C006 Final Proof page 232 232 26 .9. 2006 8:51pm Shaft Alignment Handbook, Third Edition Crosshair when viewing... proportional to the position of a core that moves through the center of the transducer as illustrated in Figure 6.23 and Figure 6.24 These devices can attain accuracies of +1% of full-scale range with stroke ranges available from 20 mils to over 20 in No current Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C006 Final Proof page 234 234 26 .9. 2006 8:51pm Shaft Alignment Handbook, Third Edition...Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C006 Final Proof page 220 220 26 .9. 2006 8:51pm Shaft Alignment Handbook, Third Edition methods will show you how to find the positions of two shaft centerlines when the machinery is not running (step 5 in Chapter 1) Once you have determined the relative positions of each shaft in a two-element drive train, the next... end to shaft end distances where accuracy of +10 mils is required Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C006 Final Proof page 222 222 26 .9. 2006 8:51pm Shaft Alignment Handbook, Third Edition The “calibrated eyeball” Looks straight enough for me Melvin Button it up and let’s get back to the shop Straightedge Taper or feeler gauges Taper gauge Feeler gauge FIGURE 6.2 Rough alignment . problem. Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C005 Final Proof page 218 26 .9. 2006 8:36pm 218 Shaft Alignment Handbook, Third Edition 6 Shaft Alignment Measuring Tools An alignment. lateral support Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C005 Final Proof page 212 26 .9. 2006 8:36pm 212 Shaft Alignment Handbook, Third Edition FIGURE 5. 51 Soft foot correction shims. relative positions of two rotating machinery shafts. In other words, these Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C006 Final Proof page 2 19 26 .9. 2006 8:51pm 2 19 methods will